Thanks both for your answers. Can't take a more detailed image of that critter because I removed it right after taking the picture, then sprayed that part with a homemade solution made of natural black soap (paste) with a little bit of vegetable oil and methanol. I use this for mealybugs and aphids, and it works. I don't like chemical insecticides, especially the organochlorine ones.

I will check if is there any improvement when I'll be back home for the weekend.

I keep coming back to this...mostly because I just cannot make heads nor tails of the image. My first reaction is to follow jalilu 's lead with the word 'grub'. I don't believe that this insect is a true grub, but could certainly be the larva of a fly (maggot), in particular that of a fruit fly.

I flashed back to my high school biology classes when I looked at that tiny white 'thing ' with the miniscule black head. Fruit fly life cycle observation imprinted the appearance of their larvae in my brain forever.

I've also wondered about leaf miner larvae, some of which are the maggots of tiny fly species.

jalilu, I am also puzzled, because I am not familiar with many insect pests on the mango.
However, there is a scale insect, Aspidiotus destructor
which, if present, would migrate to the tender growth of its host. The pest is more common on coconut palms.
You can find an image HERE.